As is known, there are available today numerous types of energy-harvesting systems, which enable recovery of energy via a mechanical system driven by a natural element, such as, for example, wind.
For instance, the U.S. Pat. No. 6,424,079, describes an energy-harvesting system, which comprises a flexible central layer, made of dielectric material, and a first layer and a second layer of piezoelectric material (polyvinylidene fluoride, PVDF). In addition, the energy-harvesting system forms a plurality of piezoelectric elements, electrically separated from one another, each of which is constituted by a pair of electrodes arranged on opposite sides of one between the first and second layers of piezoelectric material. The thickness of the central layer is comprised between 100 μm and 110 μm. Further, each of the first and second layers of piezoelectric material has a thickness comprised between 100 μm and 110 μm.
The energy-harvesting system described in the U.S. Pat. No. 6,424,079 is particularly efficient in the case where it operates within a liquid, in which case it enables harvesting of appreciable amounts of energy. However, in the case where the energy-harvesting system is immersed in a gas, the high stiffness does not enable optimization of the amount of energy recovered. In this connection, it should further be considered how the solution of reducing the stiffness by reducing the thickness of the first and second layers of piezoelectric material is not practicable. In fact, in order to exhibit a piezoelectric behaviour, PVDF must be subjected to a high tensile stress. Thus, at present a PVDF layer with piezoelectric behaviour may not have a thickness of less than about tens of micrometers; otherwise, there is the risk of failure.